This invention relates to a process for producing metallic sintered parts such as those having one or more holes penetrating along the longer direction, rod-like metallic sintered parts, e.g., round rods, shapes having different forms of cross-section, wires, etc., and thin-plate-like metallic sintered parts.
In the field of stocks such as metallic materials, plastics, rubbers, ceramics, etc., there are generally present hollow rod-like or thin-plate-like products (hereinafter referred to as "hollow material"). In the field of metallic materials to which this invention relates, hollow materials are produced by various processes such as cutting, hot extrusion, drawing, welding, etc. On the other hand, as to plastics, rubbers, ceramics, hollow materials are produced by mixing and kneading a raw material with a binder and extruding from a die while in a plastic state. But as to metallic materials, the production of hollow materials by the extrusion using a powder as a starting material like ceramics and plastics is hardly applied. This is because there have not been developed a technique for producing a starting material powder suitable for the extrusion, the selection of an organic binder used therefor and a densifying or consolidating method after the extrusion.
As to the organic binder, it is required to have a high viscosity in a small amount, to give a molded article having high strength and to show a uniform degree of dispersion. Further, it is also necessary that the removal of the organic binder after the molding is easy and harmful decomposition products are not retained. There have been proposed various thermoplastic or thermosetting resins as a binder useful for the extrusion. For example, Japanese Patent Unexamined Publication No. 113511/80 discloses the use of polyethylene, polystyrene, or acrylonitrile-butadiene-styrene copolymer together with a silane coupling agent or titanium coupling agent; Japanese Patent Unexamined Publication No. 113510/80 discloses a process for molding a ceramic powder or a metallic powder by injection or extrusion using a silane cross-linked type polyalkene resin; and Japanese Patent Unexamined Publication No. 159248/81 discloses the use of polytetramethylenephthalate as a binder. These binders are mainly organic resins, but their removal after the molding is very difficult, because, e.g., in the case of products having a thickness of about 10 mm, the temperature rising rate for the removal should be 5.degree. to 10.degree. C./hr or less in order to prevent the products from foaming and loss of their shapes.